Electrical insulating oil

ABSTRACT

The invention relates to an electrical insulating oil, resistant to oxidation and sludging, which consists essentially of a blend of about 1 to about 25 percent by volume of a solvent-extracted residue of a naphthenic petroleum distillate oil and about 75 to about 99 percent by volume of a hydrogenated naphthenic petroleum distillate oil. The solvent-extracted residue is obtained by contacting a naphthenic petroleum distillate oil with a solvent such as furfural or nitrobenzene. The hydrogenated naphthenic petroleum distillate oil is obtained by contacting a naphthenic petroleum distillate oil with hydrogen in the presence of a catalyst such as, for example, sulfides or oxides of molybdenum and at least two iron group metals.

United States Patent Rocchini et al.

[ Feb. 8, 1972 [54] ELECTRICAL INSULATING OIL [72] Inventors: Albert G.Roccltini, Oakmont; Charles E.

Trautman, Cheswick, both of Pa.

Gulf Research 8: Development Company, Pittsburgh, Pa.

22 Filed: Apr.1,1970

21 Appl. No.: 24,838

[73] Assignee:

[52] US. Cl ..252/63, 208/14, 208/18,

208/19 [51] Int. Cl. .1101!) 3/22 [58] Field ofSearch ..208/14, 18, 19;252/63 [56] References Cited UNITED STATES PATENTS 3,419,497 12/1968Rocchini et al ..252/63 2,921,011 1/1960 Ordelt et al.... .....208/143,303,125 2/1967 Martel et al ..208/264 Primary Examiner-John T.Goolkasian Assistant Examiner-Robert A. Dawson Attorney-Meyer Neishloss,Deane E. Keith and William H. Deitch ABSTRACT naphthenic petroleumdistillate oil is obtained by contacting a naphthenic petroleumdistillate oil with hydrogen in the presence of a catalyst such as, forexample, sulfides or oxides of molybdenum and at least two iron groupmetals.

10 Claims, No Drawings ELECTRICAL INSULATING OIL This invention relatesto an electrical insulating oil, and more particularly to a transformeroil which is highly resistant to oxidation and sludging.

An insulating oil to be acceptable for use in transformers must have arelatively low viscosity, usually not greater than about 85 SUS at 100F., to facilitate removal of heat from transformers by convection; arelatively high flashpoint to minimize fire hazard and evaporationlosses; and a low pour point to assure fluidity in cold weather. In viewof its use in electrical equipment, an insulating oil should also have arela-- tively high dielectric strength and a low power factor. Moreover,an electrical insulating oil should be relatively free from acid,alkali, moisture, dirt and harmful sulfur compounds which could corrodeor injure metal parts, Finally, a transformer oil of acceptable qualitymust exhibit a high degree of stability against the formation ofdeposits formed by deterioration under service conditions. Formation ofdeposits in a transformer oil is undesirable since such deposits tend tocollect on the transformer windings, thereby causing overheating, and adecrease in dielectric strength, eventually to the point of completefailure of the oil.

Transformer oils ordinarily are distillate oils refined in such manneras to secure the specified characteristics to as great an extent aspossible. While most of the desirable characteristics of an insulatingoil can be obtained from a mineral oil distillate by subjecting it tovarious refining procedures, considerable difficulty has beenencountered in producing an oil which is highly resistant to oxidationand sludging over prolonged periods of time. Many materials have beendeveloped which when added to a transformer oil greatly improve theoxidation resistance of the oil. However, a preferred transformer oil isone which is highly resistant to oxidation and sludging without theaddition of an oxidation inhibitor.

It has previously been proposed to produce an electrical insulating oilby selectively extracting the aromatic components from a mineral oildistillate with a solvent such as liquid sulfur dioxide or furfural andacid treating the raffinate with concentrated sulfuric acid or oleum.The acid treated raffinate is usually subjected to a finishing treatmentwith a solid adsorbent such as clay. It has also been proposed toproduce an electrical insulating oil by hydrogenating a highlynaphthenic distillate. Combinations of solvent extraction, acid treatingand hydrogenation with and without further finishing as with a solidadsorbent have also been proposed for producing an insulating oil. Ithas also been proposed to produce an insulating oil by blending an acidtreated naphthenic distillate with a hydrofinished naphthenicdistillate. Still further it has been proposed to produce an insulatingoil by blending a naphthenic distillate hydrogenated at a lowtemperature, i.e., 550 to 595 F., with a naphthenic distillatehydrogenated at a high temperature, i.e., 630 to 670 F. Since insulatingoils obtained by these refining methods are the product of one or moretreating procedures, disadvantages associated with such treatments areencountered. These treatments, for example, are rather costly and theygive rise to the loss of considerable amounts of oil. Furthermore, sometreated oils have a greater tendency to oxidize than untreated oils.There is some evidence, for example, that naturally occurring oxidationinhibitors in distillate oils are destroyed during some hydrogenationprocesses and that materials are formed during some hydrogenations whichgive rise to oxidation instability.

We have discovered that an electrical insulating oil which is highlyresistant to oxidation and sludging can be obtained by blending asolvent-extracted residue of a naphthenic petroleum distillate oil witha hydrogenated naphthenic petroleum distillate oil. While improvedoxidation resistance and antisludging properties are obtained byblending the solvent-extracted residue and the hydrogenated distillatewithout further treatment, optimum improvement is obtained by contactingthe blended residue and hydrogenated distillate with clay,

The solvent-extracted residue employed in the composition of theinvention has a viscosity of about 35 to about 50 SUS at 210 F. Theresidue is obtained by contacting a naphthenic petroleum distillate oilwith a solvent capable of removing polycyclic hydrocarbons and sulfurcompounds from petroleum distillate oils. Suitable solvents for thispurpose are furfural, nitrobenzene, sulfur dioxide, phenol and the like.The naphthenic petroleum distillate oil which is subjected to extractionis preferably one having an API gravity in the range of about 17 toabout 27 a boiling range within the range of about 550 to about 900 F.,a viscosity at F. in the range of about 90 to about SUS, a pour pointbelow -25 F. and a naphthene content of at least about 70 percent byvolume. An example of a preferred naphthenic distillate oil which can besubjected to solvent extraction to obtain the solvent-extracted residuehas an APl gravity of about 24 a boiling range of about 560 to about 875F., a viscosity of about 100 to about 1 10 SUS at 100 F., a pour pointbelow about -40 F., a naphthene content of about 85 percent by volumeand an aromatic content of about 15 percent by volume. The residue isadvantageously used in an amount of about 1 to about 25 percent byvolume based on the volume of the total composition,

Solvent extraction processes for refining petroleum distillate oils arewell known in the petroleum industry. Furfural, for example, has beenused as a selective solvent in removing polycyclic hydrocarbons andsulfur compounds from petroleum distillate oils. Such a process has beendescribed in a paper entitled Furfural as a Selective Solvent inPetroleum Refining by L. C. Kemp, .lr., G. B. Hamilton and H. H. Gross,Industrial and Engineering Chemistry, Vol. 40, pages 220-227 (1948). Intreating a lubricating oil with furfural, the raffinate, i.e., thelubricating oil product, has improved oxidation characteristics and animproved viscosity index. The raffinate comprises about 60 to 90 percentby volume of the original distillate charge depending upon its makeup.The material removed by the furfural, i.e., the residue, has beenconsidered to consist of undesirable constituents possessing lowoiliness, low viscosity index, poor oxidation stability, high carbonresidue and poor color. It is this so-called undesirable material, i.e.,the solvent-extracted residue which is removed from a naphthenicpetroleum distillate oil that is used to give an improved electricalinsulating oil of the present invention, The residue comprises about 10to about 40 percent by volume of the original charge depending upon itsmakeup.

The conditions employed in extracting the residue from the naphthenicpetroleum distillate oil can vary over a wide range. The solvent to oilvolume ratio, for example, can be within the range of 1:1 to 3:1,solvent to oil, respectively. The extraction temperature will depend tosome extent upon the solvent which is used. Good results are obtainedwith furfural in a countercurrent tower extraction process wherein thetemperature is within the range of about to 200 F. A residue havingexcellent properties for use in the electrical insulating oilcomposition of the invention is obtained in the countercurrentextraction of a 100 Texas distillate oil with furfural. The volume ratioof furfural to oil, respectively, is L5 to l. The temperature in thebottom of the tower is about F. The temperature in the top of the toweris about 200 F. The raffinate obtained from the top of the towercomprises about 60 to about 70 percent by volume of the distillatecharge. The residue obtained after the furfural is stripped from theextract comprises about 30 to about 40 percent by volume of thedistillate charge.

The naphthenic petroleum distillate oils which are subjected to solventextraction and hydrogenation to obtain the solvent-extracted residue andhydrogenated napthenic petroleum distillate oil, respectively, for usein the electrical insulating oil composition of the invention can bederived by conventional atmospheric distillation from any naptheniccrude oil base stock. Suitable napthenic crude oil base stocks, forexample, can be obtained from the coastal fields of Texas and Louisiana.Examples of other crude oils from which the naphthenic distillates usedin the present invention can be obtained are Bachaquero, Taparito andTia Juana crude oils, all of which are produced in western Venezuela.The naphthenic petroleum distillate oils which are subjected to solventextraction and hydrogenation can be derived from the same or differentcrude oil base stock. However, the distillates advantageously arederived from the same crude oil base stock. The distillate which issubjected to hydrogenation is preferably one having a higher APlgravity, a narrower boiling range and a lower SUS viscosity at 100 F.than the distillate which is subjected to solvent extraction.

The naphthenic petroleum distillate oil which is subjected tohydrogenation is preferably one having an API gravity in the range ofabout 25 to about 30, a boiling range within the range of about 500 toabout 750 F., a viscosity at 100 F. in the range of about 50 to about 85SUS, a pour point below about 40 F. and a naphthene content of at leastabout 70 percent by volume. An example of a preferred naphthenicdistillate oil which can be subjected to hydrogenation to form thehydrogenated naphthenic petroleum distillate oil has an AP] gravity ofabout 26 a boiling range of about 545 to about 710 F., a viscosity ofabout 58 to about 63 SUS at 100 F., a pour point below about 60 F., anaphthene content of about 80 percent by volume and an aromatic contentof about 20 percent by volume. The hydrogenated petroleum distillate oilis advantageously used in an amount of about 75 to about 99 percent byvolume based on the volume of the total composition.

The solvent-extracted residue and the hydrogenated naphthenic petroleumdistillate oil according to this invention are blended in proportions ofabout 1 to about 25 percent by volume of the solvent-extracted residuewith about 75 to about 99 percent by volume of the hydrogenateddistillate. Especially preferred blends are those containing about toabout percent by volume of the solvent-extracted residue and about 85 toabout 95 percent by volume of the hydrogenated distillate. Theproportion of the solvent-extracted residue and the hydrogenateddistillate depends somewhat upon the properties desired in the ultimatecomposition.

The hydrogenated naphthenic petroleum distillate oil is prepared bycontacting the naphthenic distallate with hydrogen in the presence of acatalyst comprising at least one hydrogenating component selected fromthe group consisting of sulfides and oxidesof (a) a combination of about2 to about percent [preferably 4 to 16 precent] by weight molybdenum andat least two iron group metals where the iron group metals are presentin such amounts that the atomic ratio of each iron group metal withrespect to molybdenum is less than about 0.4, and (b) a combination ofabout 5 to about 40 percent [preferably 10 to 25 percent] by weight ofnickel and tungsten where the atomic ratio of tungsten to nickel isabout 110.] to 5 [preferably 110.3 to 4], said hydrogenating componentbeing composited with an alumina support. Specific examples of preferredcatalysts are those containing about 2 percent nickel, 1.5 percentcobalt and 10 percent molybdenum supported on alumina, or 6 percentnickel and 19 percent tungsten supported on alumina, these catalystsbeing preferably employed in sulfided form, although they also may beemployed in the oxide form. When a sulfided catalyst is used, thecatalyst can be sulfided prior to contact with the naphthenic distillateby contacting the catalyst with a sulfiding mixture of hydrogen andhydrogen sulfide at a temperature in the range of about 550 to 650 F.either at atmospheric or elevated pressures. The catalytic hydrogenatingcomponents can be used with a variety of porous bases or supports whichmay or may not have catalytic activity of their own. Examples of suchsupports are alumina, bauxite, silica gel, as well as aluminasstabilizedwith small amounts of silica. l-lalogens, such as fluorine or chlorine,can be present in the support in combined form in amounts ranging up to0.2 or 0.5 percent by weight or more. Other suitable supports can alsobe used. These catalyst components can be prepared in known manner.Especially advantageous results are obtained when the hydrogenationtreatment is carried out at an average catalyst bed temperature of about575 to about 645 F., especially 600 to 635 F.. and under a combinationof conditions effective to produce appreciable consumption of hydrogenbut no substantial cracking. However, the process can be carried out athigher temperatures, up to about 750 F. with acceptable results. it ispreferred to employ reaction pressures in the range of about 1,000 toabout 2,000 p.s.i.g., but other pressures in the range of about 500 toabout 3,000 p.s.i.g. can be used. The oil is preferably contacted withthe catalyst in a ratio of about 1.5 to about 3 volumes of liquid perhour per volume of catalyst, but other ratios in the range of about 0.5to about 4 liquid volumes per hour per volume of catalyst can be used.The reaction conditions employed in the catalyst bed are interrelated tothe extent that the more severe treating conditions of temperature andpressure are normally more useful with higher space velocities.Conversely, less severe conditions of temperature and pressure arenormally more useful with space velocities in the lower part of therange disclosed. By way of example, excellent results are obtainable atan average catalyst bed temperature of about 600 R, an operatingpressure of about 1,000 p.s.i.g. and at a space velocity of about 1.5liquid volumes of oil per hour per volume of catalyst; similarly, goodresults are also obtainable at an average catalyst bed temperature ofabout 640 F., a reaction pressure of about 1,735 p.s.i.g. and at a spacevelocity of about 3 liquid volumes of oil per hour per volume ofcatalyst. The hydrogen-containing gas to oil ratio employed in thehydrogenation reaction is preferably in the range of about 1,000 to3,000 SCF/Bbl., but other ratios can be used, for example, the gas tooil ratio can be as low as 500 SCF/Bbl. or as great as 4,000 SCF/Bbl.Very satisfactory results have been obtained with hydrogen of about topercent purity that has been generated in a platinum reforming reaction,but the hydrogen employed in the process need not be of this purity and,in fact, can be as low as 70 percent hydrogen or less, for example, 60percent. I

Following hydrogenation of the naphthenic distillate oil, thehydrogenated oil is degassed to remove light hydrocarbons and dissolvedgases including hydrogen sulfide and ammonia. The degassed hydrogenateddistillate is preferably dried to give a low moisture content.

The dried hydrogenated distillate can be clay treated and then blendedwith the solvent-extracted residue or the clay treating can be performedafter the components have been blended. We prefer to blend thesolvent-extracted residue with the hydrogenated distillate and thensubject the entire blend to clay contacting or percolation.

Clay contacting and percolation are well-known petroleum processes andinvolve decolorizing and stabilizing the oils by contact with finelydivided clays. Clay contacting consists of rapid batch mixing of the oiland finely ground 200 mesh) activated clay followed by filtration toremove the clay. Clay percolation comprises filtering or percolating theoil through a bed of rather coarse (16 to 60 mesh) clay. in claycontacting, the clay life may be in the order of 30 to barrels of oilper ton of clay at temperatures up to about 300 F. In clay percolationor filtration, the clay life may be in the order of 100 to 400 barrelsof oil per ton of clay at ambient or moderately elevated, i.e., 100 to200 F., temperatures. Clays of the kind normally used in clay finishing,including fullers earth, bauxite, Millwhite, Attapulgus or Filtrol canbe employed.

The preparation of a suitable hydrogenated petroleum distillate oil foruse in the insulating oil of the present invention is illustrated by thefollowing specific embodiment. in this embodiment, the charge stock is anaphthenic distillate oil boiling in the range of about 546 to about 710F. derived from a coastal (Texas) crude oil. The naphthenic distillateoil charge stock has the following typical inspections:

Naphthenic Distillate Charge Stock for Hydrogenation inspectionsGravity. API 25.9

Viscosity: SUS

at 100 F. 59.4

at 210 F. 34.3 lnterfacial Tension.

77 F.. Dynes/cm. 37.2 Flashpoint: OC. F. 300 Fire Point: C. F. 325 PourPoint. F. -oo Color. ASTM D1500 1.0 Sulfur. ASTM D1552. 7: 0.19 BombSludge. ASTM D1313. 0.19 Neutruliwation No.. ASTM D974 Total Acid No.1.3 Iodine No. 11.5 Aniline Point. F. 149 Hydrocarbon Type Analysis: ABy weight Alkanes 0.0

Noncondensed Cycloalkanes 44.5

Condensed Cycloalkanes 35.0

Aromatics 20.5

In this embodiment, the naphthenic charge stock is contacted withhydrogen in a reactor wherein the average reactor temperature is 600 F.,the pressure is 1,000 p.s.i.g., the space velocity is 1.5 liquid volumesof oil per hour per volume of catalyst and the gas circulation rate is2,000 SCF/Bbl. The catalyst employed is l/l2-inch diameter extrudates ofnickel, cobalt and molybdenum on an alumina support. A typical sample ofthe fresh catalyst has about 2.4 percent nickel, about 1.28 percentcobalt. about 9.85 percent molybdenum and about 0.03 percent chlorine.The catalyst is prepared by impregnation of the alumina support withwater-soluble salts of the metals and calcining. The catalyst issulfided by contact at reaction conditions with a West Texas furnace oilcontaining about 0.8 percent sulfur. This catalyst typically has adensity of about 51.2 lbs./cu.ft. After degasification of thehydrogenated product. it is filtered through Attapulgus clay at roomtemperature in a proportion of about 100 barrels of oil per ton of clayat a rate of about 0.5 barrel of oil per hour per ton of clay. Typicalinspections of the unfiltered and the clay filtered hydrogenatednaphthenic distillate are as follows:

Hydrogenated Naphthenic Distillates Inspections Unfiltered Clay FilteredGravity. API 27.2 27.2 Viscosity. SUS

at 100 F. 58.3 58.3

at210 F. 34.1 34.1

lnterlacial Tension.

77 F.. Dynes/cm. 44 51 Flashpoint. 0C. F. 315 300 Fire Point: 0C. F. 325320 Four Point. F. -65 -65 Power Factor.

ASTM D924, r

at 77 F. 0.01 0.01

at 212 F. 0.16 0.09 Dielectric Strength.

ASTM D877. KV. 38 45 Color. ASTM D1500 0.5 0.5 Sulfur. ASTM D1552. 7:0.05 0.05 Bomb Sludge,

ASTM D1313.'/( 3.40 0.18 Neutralization No.

ASTM D974 Total Acid N0. 0.03 0.0] Iodine No. 9.0 9.4 Aniline Point. F.154.4 154.4 Oxidation Test.

ASTM D2440 164 hrs.:

Sludge. "/1 9.9 4.4

Neutralization No. 7.4 5.4

From the foregoing data, it will be noted that clay treating thehydrogenated distillate improves its power factor at 212 F. anddielectric strength. also its bomb sludge and oxidation stability byASTM D2440. It is to be particularly noted that the charge stockdistillate had a bomb sludge of 0.19 percent and that the hydrogenateddistillate prior to clay filtration had a bomb sludge of 3.4 percent.After clay filtering. the hydrogenated distillate had a bomb sludge(0.18 percent) about the same as the charge stock initially.

The preparation of a suitable solvent-extracted residue for use in theinsulating oil composition ofthe present invention is illustrated by thefollowing specific embodiment. In this embodiment. the charge stock is anaphthenic distillate oil boiling in the range of about 560 to about 872F. derived from a coastal (Texas) crude oil. The naphthenic distillatecharge stock has the following typical inspections:

Naphthenic Distillate Charge Stock for Solvent Extraction Aromatics 15In this embodiment, the naphthenic charge stock is introduced into apacked, vertical extraction tower wherein countercurrent flow withfurfural takes place. The furfural is introduced near the top of thetower. Naphthenic charge stock is introduced near the bottom of thetower. The temperature at the bottom of the tower is about 160 F. Thetemperature at the top of the tower is about 200 F. The furfural tonaphthenic charge stock volume ratio is about 1.5 to 1. furfural tonaphthenic charge stock, respectively. The yield of raffinate is 63percent by volume. The yield of extractedresidue after removal of thefurfural is 37 percent by volume. The extracted residue has thefollowing typical properties:

Inspections Solvent-Extracted Residue Gravity. API 16.8 Viscosity: SUS

at F. 144

210 F. 40 Flashpoint: OC. F. 315 Fire point: 0C. F. 345 Four point. F.35 Sulfur. ASTM D1552. "/t 0.29 Iodine No. 13.1 Aniline point. F. 97

and also for the clay-filtered blend of solvent-extracted residue (10percent by volume) and hydrogenated distillate (90 percent by volume).

TABLE I A B C l o 't'on, ereent by volume: O glfio g eiiate naphthenicdistillate- 100 100 90 SoIYent-extraQted residue 10 Ins ect ons:

Gravity, API 27. 2 27. 2 26.1

' S t: ititi fii i "i 58.3 58.3 60.9 210 F 34. 1 34. 1 34.6 Interfaeialtension, 77 F., dynes/cm 44 51 45 Flash point: 00. F 315 300 300 Firepoint: 00, F- 325 320 315 Pour point, fis ffiija .55.}... 65 -65 -65erce a i ii fi R 0.01 0.01 0. 01 212 F 0.16 0.09 0.10 Dielectricstrength, ASTM D877, kv 38 46. 53 Color, ASTM D1500 0. 5 0. 5 1. 0Sulfur, ASTM D1552, percent 0.05 0.05 0.08 Bomb sludge, ASTM D1313,percent. 3.40 0.18 0.04 Neutralization N0. ASTM D974, total acid No 0.030.01 0.06 Iodine No 9.0 9.4 10.0 Aniline point, F. 154. 4 154. 4 152.1Oxidation test, AST D2440 164 hrs:

Sludge, percent 9. 9 4. 4 0.13 Neutralization No 7.4 5. 0.54

Clay filtered-100 barrels of oil composition per ton of clay at ambienttemperature at a rate of about 0.5 barrel of oil per hour per tonoiclay;

it is evident from the test results reported in Table I that theoxidation stability of the blended composition of the invention(Composition C) is greater than the oxidation stability of either thehydrogenated oil (Composition A) or the clay filtered hydrogenated oil(Composition B). It is to be noted further that the dielectric strength(ASTM D877) and the bomb sludge (ASTM D1313) of the composition of theinvention (Composition C) are improved over the correspondinginspections on the hydrogenated oil (Composition A) and clay filteredhydrogenated oil (Composition B).

Although the electrical insulating oils prepared according to thepresent invention are highly resistantto oxidation and sludging, theoils have good response to the addition of an oxidation inhibitor andsuch an inhibitor can be employed if desired. Examples of suitableoxidation inhibitors which can be employed include the polyalkyl arylhydroxy compounds, e.g., 2,6-ditertiary butyl-4-methylphenol,2,4-dimethyl-6-tertiary octylphenol andbis(2-hydroxy-3-l-butyl-5-methylphenyl)methane, etc., as well as thevarious amines, e.g., diphenylamine, phenyl beta naphthylamine, etc.When these oxidation inhibitors are used, they are generally employed inamounts of about 0.01 to about l.0 percent by weight or more.

While the oil compositions of the invention are primarily useful aselectrical insulating oils, it will be understood that they can be usedas lubricants in some instances. When used as lubricants they may alsocontain an oxidation inhibitor and other additives normally used inlubricating oils including a detergent, an oiliness and extreme pressureagent, a viscosity index improver, a pour point depressant, an antirustagent, a corrosion inhibitor, an antifoam agent and the like in varyingproportions.

While our invention has been described with reference to variousspecific examples and embodiments, it will be understood that theinvention is not limited to such examples and embodiments and may bevariously practiced within the scope of the claims hereinafter made.

We claim:

1. An electrical insulating oil consisting essentially of a blend of:

A. about i to about 25 percent by volume of a residue having a viscosityof about 35 to about 50 SUS at 2l0 F., said residue being the productwhich remains after removing solvent from the extract obtained byextracting a naphthenic petroleum distillate oil having an API gravityin the range of about 17 to about 27 a boiling range within the range ofabout 550 to about 900 F., a viscosity at 100 F. in the range of aboutto about I20 SUS, a pour point below -25 F. and a naphthene content ofat least about 70 percent by volume with a solvent capable of removingpolycyclic hydrocarbons and sulfur compounds from petroleum distillateoils and about 75 to about 99 percent by volume of a hydrogenatednaphthenic petroleum distillate oil, said hydrogenated naphthenicpetroleum distillate oil being obtained by contacting a naphthenicpetroleum distillate oil having an API gravity in the range of about 25to about 30 a boiling range within the range of about 500 to about 750F., a viscosity at l00 F. in the range of about 50 to about 85 SUS, apour point below about 40 F. and a naphthene content of at least about70 percent by volume with hydrogen in the presence of a catalystcomprising at least one hydrogenating component selected from the groupconsisting of sulfides and oxides of (a) a combination of about 2 toabout 25 percent by weight of molybdenum and at least two iron groupmetals where the iron group metals are present in such amounts that theatomic ratio of each iron group metal with respect to molybdenum is lessthan about 0.4, and (b) a combination of about 5 to about 40 percent byweight of nickel and tungsten where the atomic ratio of tungsten tonickel is about 1:01 to 5, said hydrogenating component being compositedwith an alumina support, said contacting being carried out at an averagecatalyst temperature of about 575 to about 750 F., at a space velocityof about 0.5 to about 4 liquid volumes of oil per volume of catalyst perhour, and at a pressure of about 500 to about 3,000 p.s.i.g.

2. An electrical insulating oil in accordance with claim I wherein theblend consists of about 5 to about 15 percent by volume of thesolvent-extracted residue and about 85 to about percent by volume of thehydrogenated distillate.

3. An electrical insulating oil in accordance with claim I wherein theblend of solvent-extracted residue and the hydrogenated distillate iscontacted with clay.

4. An electrical insulating oil in accordance with claim 1 wherein thesolvent used in obtaining the solvent-extracted residue is furfural andthe hydrogenating component of the catalyst used in obtaining thehydrogenated naphthenic petroleum distillate is a sulfided combinationof nickel, cobalt and molybdenum.

S. An electrical insulating oil in accordance with claim 1 wherein thesolvent used in obtaining the solvent-extracted residue is furfural andthe hydrogenating component of the catalyst used in obtaining thehydrogenated naphthenic petroleum distillate is a sulfided combinationof nickel and tungsten.

6. An electrical insulating oil consisting essentially of a clay treatedblend of;

A. about 5 to about 15 percent by volume ofa residue having a viscosityof about 35 to about 50 SUS at 210 F., said residue being the productwhich remains after removing furfural from the extract obtained byextracting a naphthenic petroleum distillate oil having an API gravityof about 24, a boiling range within the range of about 560 to about 875F., a viscosity at 100 F. in the range of about 100 to about ll0 SUS, apour point below about -40 F. and a naphthene content of about 85percent by volume with furfural and B. about 85 to about 95 percent byvolume of a hydrogenated naphthenic petroleum distillate oil, saidnaphthenic petroleum distillate oil having an API gravity of about 26, aboiling range of about 545 to about 7 l 0 F., a viscosity at 100 F. inthe range of about 58 to about 63 SUS, a pour point below about -60 F.and a naphthene content of about 80 percent by volume; said hydrogenatednaphthenic petroleum distillate oil being produced by contacting anaphthenic petroleum distillate oil with hydrogen in the presence of acatalyst comprising a sulfided combination of about 4 to 16 percent byweight of nickel, cobalt and molybdenum, said contacting being carriedout at an average catalyst temperature of about 575 to about 645 F., ata space velocity of about 1.5 to about 3 liquid volumes of oil pervolume of catalyst per hour, and at a pressure of about 1,000 p.s.i.g.

7. An electrical insulating oil in accordance with claim 6 wherein thesolvent-extracted residue and the hydrogenated distillate are derivedfrom the same naphthenic crude oil base stock.

8. An electrical insulating oil in accordance with claim 6 wherein theclay treated blend is obtained by filtering the

2. An electrical insulating oil in accordance with claim 1 wherein theblend consists of about 5 to about 15 percent by volume of thesolvent-extracted residue and about 85 to about 95 percent by volume ofthe hydrogenated distillate.
 3. An electrical insulating oil inaccordance with claim 1 wherein the blend of solvent-extracted residueand the hydrogenated distillate is contacted with clay.
 4. An electricalinsulating oil in accordance with claim 1 wherein the solvent used inobtaining the solvent-extracted residue is furfural and thehydrogenating component of the catalyst used in obtaining thehydrogenated naphthenic petroleum distillate is a sulfided combinationof nickel, cobalt and molybdenum.
 5. An electrical insulating oil inaccordance with claim 1 wherein the solvent used in obtaining thesolvent-extracted residue is furfural and the hydrogenating component ofthe catalyst used in obtaining the hydrogenated naphthenic petroleumdistillate is a sulfided combination of nickel and tungsten.
 6. Anelectrical insulating oil consisting essentially of a clay treated blendof: A. about 5 to about 15 percent by volume of a residue having aviscosity of about 35 to about 50 SUS at 210* F., said residue being theproduct which remains after removing furfural from the extract obtainedby extracting a naphthenic petroleum distillate oil having an APIgravity of about 24* , a boiling range within the range of about 560* toabout 875* F., a viscosity at 100* F. in the range of about 100 to about110 SUS, a pour point below about - 40* F. and a naphthene content ofabout 85 percent by volume with furfural and B. about 85 to about 95percent by volume of a hydrogenated naphthenic petroleum distillate oil,said naphthenic petroleum distillate oil having an API gravity of about26* , a boiling range of about 545* to about 710* F., a viscosity at100* F. in the range of about 58 to about 63 SUS, a pour point belowabout - 60* F. and a naphthene content of about 80 percent by volume;said hydrogenated naphthenic petroleum distillate oil being produced bycontacting a naphthenic petroleum distillate oil with hydrogen in thepresence of a catalyst comprising a sulfided combination of about 4 to16 percent by weight of nickel, cobalt and molybdenum, said contactingbeing carried out at an average catalyst temperature of about 575* toabout 645* F., at a space velocity of about 1.5 to about 3 liquidvolumes of oil per volume of catalyst per hour, and at a pressure ofabout 1,000 p.s.i.g.
 7. An electrical insulating oil in accordance withclaim 6 wherein the solvent-extracted residue and the hydrogenateddistillate are derived from the same naphthenic crude oil base stock. 8.An electrical insulating oil in accordance with claim 6 wherein the claytreated blend is obtained by filtering the combined solvent-extractedresidue and hydrogenated distillate at ambient temperature through abody of 16 to 60 mesh clay in a proportion of aBout 100 to about 400barrels of oil per ton of clay.
 9. An electrical insulating oilcomprising a major proportion of the clay treated blend of claim 8 andfrom 0.01 to 1.0 percent by weight of an oxidation inhibitor.
 10. Anelectrical insulating oil comprising a major proportion of the claytreated blend of claim 8 and a minor oxidation inhibiting amount of2,6-ditertiary butyl-4-methylphenol.